1. Technical Field
The present invention relates to a power amplifier circuit.
2. Background Art
In a power amplifier circuit used for a transmitter or the like of radio communication equipment, in order to keep an output of the transmitter constant, the change in an output of a power amplifier is monitored, and the change is fed back to an input level thereof.
FIG. 15 a diagram showing a power amplifier circuit which is generally and widely used and is disclosed in Japanese Patent Application Laid-Open No. 2004-072556. The power amplifier circuit includes a variable attenuator (ATT) 21, an amplifier 22, a directional coupler (D-CPL) 23, a detector (DET) 24, a resistor 25, an operational amplifier (OP-AMP) 26, a reference voltage source (REF) 27 and a low pass filter (LPF) 28.
An output of the amplifier 22 is detected by the DET 24 through the D-CPL 23. The OP-AMP 26 outputs a difference between an output of the DET 24 and a reference voltage of the REF 27. The output is fed back negatively to the ATT 21 through the LPF 28 which is a loop filter performing phase compensation. Thereby output power of the amplifier 22 is kept constant. The power amplifier circuit includes the D-CPL 23 on an output side of the amplifier 22. Accordingly, when the output power amplified by the amplifier 22 passes through the D-CPL 23, a part of the output power is branched and enter the DET 24. As a result, an electric power is wasted.
FIG. 16 shows a diagram showing other power amplifier circuit of a related art of the present invention, which is disclosed in Japanese Patent Application Laid-Open No. 2007-005876. In the power amplifier circuit shown in FIG. 16, a level control function and an electric power amplifying function provided in the amplifier 22 shown in FIG. 15 are separated. That is, the amplifier 22 performs a level control and a power amplifier 29 amplifying a power is arranged on an output side of the D-CPL 23. In the circuit configuration, a loss can be reduced, since the D-CPL 23 is set on an input side of the power amplifier 29. Thereby, the power amplifier shown in FIG. 16 can highly improve efficiency in power consumption.
FIG. 17 shows a diagram showing another power amplifier circuit of a related art of the present invention. In the power amplifier circuit shown in FIG. 17, a power supply (PS) 30 for controlling a transmission output is connected to the power amplifier 29 shown in FIG. 16. The power amplifier circuit shown in FIG. 17 controls a voltage which the PS 30 supplies to the power amplifier 29 according to a transmission output.
Japanese Patent Application Laid-Open No. 2003-244001, Japanese Patent Application Laid-Open No. 2004-221737 and Japanese Patent Application Laid-Open No. 2005-117315 disclose a related art of the power amplifier circuit which includes a pre-amplifier and a post-power amplifier, and changes a voltage supplied to the post-power amplifier to improve efficiency.